title: The role of C9 in complement-mediated killing of Neisseria.
abstract: During the routine examination of a healthy 31-yr-old woman, we found an incomplete deficiency of the 9th component of complement (C9). By hemolytic assay her serum C9 activity was 10 to 15% of normal. Limited family studies suggested that she inherited the deficiency as an autosomal codominant trait. She had no history of unusual or severe infections. When tested for bactericidal activity against serum-sensitive Neisseria gonorrhoeae and N. meningitidis, her serum reacted comparably to normal serum. Normal serum depleted immunochemically of C9 and sera from congenitally C9-deficient patients were also bactericidal against serum-sensitive Neisseria but required 120 min to kill the same numbers of gonococci that intact serum killed within 30 min. In the electron microscope, N. gonorrhoeae incubated with C9-depleted serum were fragmented but lacked the typical C lesions. Therefore, serum lacking C9 can kill serum-sensitive Neisseria, unlike sera deficient in the other terminal C components.
mesh_terms: D000328:Adult; D001770:Blood Bactericidal Activity; D003186:Complement C9 / Q000172:deficiency*; D003165:Complement System Proteins / Q000378:metabolism*; D003602:Cytotoxicity, Immunologic; D005260:Female; D006461:Hemolysis; D006462:Hemolytic Plaque Technique; D006801:Humans; D005779:Immunodiffusion; D007164:Immunosorbents; D009343:Neisseria; D009344:Neisseria gonorrhoeae / Q000648:ultrastructure
chemical_list: D003186:Complement C9; D007164:Immunosorbents; D003165:Complement System Proteins